CN113754920A - Polyimide composite aerogel, preparation method and application of polyimide composite aerogel as solar evaporator - Google Patents
Polyimide composite aerogel, preparation method and application of polyimide composite aerogel as solar evaporator Download PDFInfo
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- CN113754920A CN113754920A CN202111159750.XA CN202111159750A CN113754920A CN 113754920 A CN113754920 A CN 113754920A CN 202111159750 A CN202111159750 A CN 202111159750A CN 113754920 A CN113754920 A CN 113754920A
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- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/28—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a liquid phase from a macromolecular composition or article, e.g. drying of coagulum
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
- F24S20/00—Solar heat collectors specially adapted for particular uses or environments
- F24S20/20—Solar heat collectors for receiving concentrated solar energy, e.g. receivers for solar power plants
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2205/00—Foams characterised by their properties
- C08J2205/02—Foams characterised by their properties the finished foam itself being a gel or a gel being temporarily formed when processing the foamable composition
- C08J2205/026—Aerogel, i.e. a supercritically dried gel
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- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2379/00—Characterised by the use of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing nitrogen with or without oxygen, or carbon only, not provided for in groups C08J2361/00 - C08J2377/00
- C08J2379/04—Polycondensates having nitrogen-containing heterocyclic rings in the main chain; Polyhydrazides; Polyamide acids or similar polyimide precursors
- C08J2379/08—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
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- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K3/00—Use of inorganic substances as compounding ingredients
- C08K3/38—Boron-containing compounds
- C08K2003/382—Boron-containing compounds and nitrogen
- C08K2003/385—Binary compounds of nitrogen with boron
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- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K3/00—Use of inorganic substances as compounding ingredients
- C08K3/02—Elements
- C08K3/04—Carbon
- C08K3/041—Carbon nanotubes
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K7/00—Use of ingredients characterised by shape
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
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- C08K9/04—Ingredients treated with organic substances
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A20/00—Water conservation; Efficient water supply; Efficient water use
- Y02A20/124—Water desalination
- Y02A20/138—Water desalination using renewable energy
- Y02A20/142—Solar thermal; Photovoltaics
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/40—Solar thermal energy, e.g. solar towers
Abstract
A polyimide composite aerogel, a preparation method and application thereof as a solar evaporator relate to the field of solar-driven water evaporation aerogel and preparation thereof. The modified boron nitride modified polyimide film is formed by uniformly dispersing dopamine modified boron nitride and hydroxylated carbon nanotubes in a polyimide matrix, and presents a low-bending vertical pipe hole structure. Firstly, carrying out surface modification treatment on boron nitride by adopting dopamine, then adding polyamic acid into a mixed solution of the dopamine modified boron nitride and a hydroxylated carbon nanotube, taking liquid nitrogen as a cold source, carrying out freeze forming by a four-directional process, and sequentially carrying out vacuum freeze drying and imidization to obtain the composite aerogel. The composite aerogel has excellent hydrophilicity, high temperature resistance, high-efficiency water transportation capacity and high-efficiency photo-thermal conversion capacity. The composite aerogel has high-efficiency solar evaporation rate and purification capacity on sewage containing high-concentration metal ions as a solar evaporator, and has wide application prospects in the fields of sewage treatment and seawater desalination.
Description
Technical Field
The invention relates to the field of solar-driven water evaporation aerogel and preparation thereof, in particular to polyimide composite aerogel, a preparation method and application of the polyimide composite aerogel as a solar evaporator.
Background
With the continuous deepening of the industrialization process, the problem of water resource pollution becomes more and more serious. The effective utilization of abundant and clean solar energy for sewage evaporation and purification and seawater desalination is one of the important ways to solve the problem of clean water. The existing photothermal conversion material for solar water evaporation mainly comprises a membrane material, hydrogel, aerogel and the like, wherein the aerogel is widely concerned due to the characteristics of low density, high porosity, rich network-shaped porous channels and the like. Thereby through structural design with the aerogel that obtains to have special pore structure the transportation speed of improvement water, thereby through the evaporation that promotes the hydrone that improves aerogel surface light-heat conversion efficiency, improve the mechanical properties and the safety in utilization of aerogel material through the composite technology, domestic and foreign scholars have carried out extensive and intensive research to this, still need to improve the comprehensive properties of aerogel solar evaporator. In addition, the aerogel precursor is placed in a cold source such as liquid nitrogen, and the preparation process is simple and easy to implement, and is an important way for obtaining various porous structures and ultralight aerogels. Generally, aerogels prepared by the method have a three-dimensional network structure which is communicated with each other, and the structure is not beneficial to transpiration of moisture, so that water transportation in a solar-driven water evaporation process is limited to a certain extent.
Polyimide aerogel has excellent mechanical properties, high temperature resistance and other properties, and has very wide application in the fields of aerospace and the like, but the application of the aerogel in a solar evaporator is severely limited by the defects of hydrophobicity, low solar energy conversion efficiency and the like. The hydrophilic performance of the polyimide aerogel can be improved by adding hydrophilic nanoparticles and grafting hydrophilic functional groups on the surface; the photo-thermal conversion efficiency of the polyimide aerogel can be improved by adding metal particles, carbon-based materials (such as carbon nanotubes, graphene oxide and the like), semiconductor materials and the like; through the optimal design aerogel synthesis technology, the polyimide aerogel vertical pipe hole structure with low curvature can be endowed, the transpiration effect is effectively enhanced, and the transportation speed of water is improved.
The polyimide/dopamine modified boron nitride/hydroxylated carbon nanotube composite aerogel used as the solar evaporator is prepared, the dopamine modified boron nitride endows the aerogel with excellent hydrophilic performance and high temperature resistance, the hydroxylated carbon nanotube endows the aerogel with excellent photo-thermal conversion capability, liquid nitrogen is used as a cold source, the composite aerogel with a low-curvature vertical tube hole structure is obtained through a four-directional process, and the transpiration effect in the water transportation process is effectively improved.
Disclosure of Invention
In order to overcome the above defects in the prior art, an object of the present invention is to provide a polyimide composite aerogel, which is formed by uniformly dispersing dopamine-modified boron nitride and hydroxylated carbon nanotubes in a polyimide matrix, has a low-curvature vertical pore structure, and has excellent hydrophilicity, high temperature resistance, and high-efficiency water transport capacity and light-heat conversion capacity.
Another object of the present invention is to provide a method for preparing a polyimide composite aerogel, comprising the following steps:
the method comprises the following steps: preparation of dopamine modified boron nitride
Dissolving tris powder in deionized water, adjusting the pH value of the solution by using dilute hydrochloric acid, then adding a hydroxylated boron nitride nanosheet, dopamine hydrochloride and ammonium persulfate into the solution, stirring uniformly by using ultrasonic waves, continuing stirring and reacting under the condition of water bath heat preservation, and finally washing and drying to obtain dopamine modified boron nitride powder;
step two: preparation of polyimide/dopamine modified boron nitride/hydroxylated carbon nanotube composite aerogel
Respectively dispersing dopamine modified boron nitride powder and a hydroxylated carbon nanotube into deionized water, mixing and ultrasonically stirring uniformly, then adding polyamide acid into the mixed dispersion liquid, adding triethylamine, stirring and dissolving completely, adopting a four-directional preparation process, freezing and molding the mixed solution in a mold by using liquid nitrogen, and then sequentially carrying out vacuum freeze drying and imidization to obtain the polyimide/dopamine modified boron nitride/hydroxylated carbon nanotube composite aerogel.
The preferable technical proposal of the preparation method is as follows:
in the first step, the concentration of a tris solution is 1-1.5 g/L, the mass ratio of tris powder to hydroxylated boron nitride nanosheets is 2-3: 10, the pH value of the tris solution is adjusted to 4-5 by 1mol/L of dilute hydrochloric acid, the mass ratio of the hydroxylated boron nitride nanosheets, dopamine hydrochloride and ammonium persulfate is 25: 10: 6, and the mixture is subjected to ultrasonic stirring uniformly and then is continuously stirred and reacted for 10-14 hours under the condition of water bath heat preservation at 55-65 ℃.
In the second step, the mass ratio of the polyamic acid to the triethylamine is 1: 1, the mass ratio of the polyamic acid to the dopamine modified boron nitride + hydroxylated carbon nanotube is 80: 20, and the mass ratio of the dopamine modified boron nitride to the hydroxylated carbon nanotube is 3-19: 1. Adopting a four-orientation preparation process, freezing the mixed solution in the mold for 15-60 min by using liquid nitrogen for molding, then carrying out vacuum freeze drying for 48-96 h, carrying out imidization reaction in a tube furnace under the protection of nitrogen after vacuum freeze drying, wherein the imidization conditions are as follows: heating the sample from room temperature to 80 ℃, 150 ℃ and 250 ℃ in sections at a heating rate of 8 ℃/min, and continuously preserving heat for 1h in each section to finally obtain the polyimide/dopamine modified boron nitride/hydroxylated carbon nanotube composite aerogel.
As a further object of the invention, the invention provides an application of the polyimide composite aerogel as a solar evaporator, which has high water evaporation rate and metal ion purification capability on sewage containing high-concentration metal ions.
Compared with the prior art, the invention has the beneficial effects that:
1) the preparation method of the polyimide composite aerogel is simple, and the aerogel can be effectively controlled to have a low-curvature vertical pipe hole structure, so that the transpiration effect of water is improved.
2) The polyimide/dopamine modified boron nitride/hydroxylated carbon nanotube composite aerogel prepared by the invention has excellent hydrophilic property and high temperature resistance.
3) The polyimide/dopamine modified boron nitride/hydroxylated carbon nanotube composite aerogel prepared by the invention has high-efficiency solar evaporation rate and purification capacity on sewage containing high-concentration metal ions as a solar evaporator, and has wide application prospects in the fields of sewage treatment and seawater desalination.
Drawings
Fig. 1 is a schematic view of a four-directional freezer.
Fig. 2 is a graph of water contact angle as a function of time for aerogels prepared in example 1, example 2, and example 4.
Fig. 3a and b are SEM photographs (both from the perspective of the plane of the Z-Y axis in fig. 1) of the aerogels prepared in example 3 and example 4, respectively.
FIG. 4 is at 2kW/m2The surface temperature of the aerogels prepared in examples 1, 2 and 4 under xenon light exposure is plotted against time.
FIG. 5 is a graph showing the comparison of ion concentrations before and after the purification of high-concentration metal ion wastewater by the aerogel prepared in example 4.
FIG. 6 is at 2kW/m2Under xenon lamp illumination, examples 1, 3, 4 and examples5 water evaporation rate of the aerogels prepared are compared.
Detailed Description
The present invention will be described in further detail with reference to the following examples and accompanying drawings.
Example 1
Adding 1.35g of polyamic acid and 1.485ml of triethylamine into 54ml of deionized water, stirring and dissolving completely, pouring the solution into a mold, placing the mold in a four-directional freezing device for freezing for 30min for molding, then transferring the mold into a vacuum freeze dryer for processing for 72 hours, taking out a sample, placing the sample in a tubular furnace, and carrying out imidization reaction under the protection of nitrogen. The imidization condition is that the sample is heated to 80 ℃, 150 ℃ and 250 ℃ in sections at the speed of 8 ℃/min from room temperature, and the temperature is kept for 1 hour in each section continuously, so as to obtain the polyimide aerogel.
Example 2
The method comprises the following steps: 0.12g of tris powder was dissolved in 100ml of deionized water and the solution pH was adjusted to 4.5 with dilute hydrochloric acid. The solution was then transferred to a three-necked flask and 0.5g of hydroxylated boron nitride, 0.2g of dopamine hydrochloride and 0.12g of ammonium persulfate were added thereto in mass ratio. And (3) after the mixed solution is uniformly stirred by ultrasound, stirring and reacting for 10 hours under the condition of water bath heat preservation at the temperature of 60 ℃, filtering and washing by using deionized water, and drying for 10 hours at the temperature of 80 ℃ to obtain the dopamine modified boron nitride.
Step two: 1.08g of polyamic acid and 1.485ml of triethylamine were added to 54ml of 5mg/ml dopamine modified boron nitride dispersion, wherein the mass ratio of polyamic acid to dopamine modified boron nitride was 80: 20.
And after completely stirring and dissolving, pouring the solution into a mold, placing the mold in a four-directional freezing device for freezing for 30min for molding, then transferring the mold into a vacuum freeze dryer for processing for 72 hours, taking out a sample, placing the sample in a tubular furnace, and carrying out imidization under the protection of nitrogen. The imidization condition is that the sample is heated to 80 ℃, 150 ℃ and 250 ℃ in sections at the speed of 8 ℃/min from room temperature, and the temperature is continuously kept for 1 hour in each section, so as to obtain the polyimide/dopamine modified boron nitride aerogel.
Example 3
The method comprises the following steps: 0.12g of tris powder was dissolved in 100ml of deionized water and the solution pH was adjusted to 4.5 with dilute hydrochloric acid. The solution was then transferred to a three-necked flask and 0.5g of hydroxylated boron nitride, 0.2g of dopamine hydrochloride and 0.12g of ammonium persulfate were added thereto in mass ratio. And (3) after the mixed solution is uniformly stirred by ultrasound, stirring and reacting for 10 hours under the condition of water bath heat preservation at the temperature of 60 ℃, filtering and washing by using deionized water, and drying for 10 hours at the temperature of 80 ℃ to obtain the dopamine modified boron nitride.
Step two: 1.08g of polyamic acid was added to a beaker containing 40.5ml of a 5mg/ml dopamine-modified boron nitride dispersion and 13.5ml of a 5mg/ml hydroxylated carbon nanotube dispersion, and 1.485ml of triethylamine was added thereto and stirred. Wherein the mass ratio of the polyamic acid to the dopamine modified boron nitride to the hydroxylated carbon nanotube is 80: 15: 5.
After the solution is completely dissolved by stirring, pouring the solution into a mold, placing the mold in a low-temperature cold well (-40 ℃) for conventional freezing for 6h for molding, then transferring the mold into a vacuum freeze dryer for processing for 72 h, taking out a sample, placing the sample in a tubular furnace, and carrying out imidization under the protection of nitrogen. The imidization condition is that the sample is heated to 80 ℃, 150 ℃ and 250 ℃ in sections at the speed of 8 ℃/min from room temperature, and the temperature is continuously kept for 1 hour in each section, so as to obtain the polyimide/dopamine modified boron nitride/hydroxylated carbon nanotube composite aerogel.
Example 4
The method comprises the following steps: 0.12g of tris powder was dissolved in 100ml of deionized water and the solution pH was adjusted to 4.5 with dilute hydrochloric acid. The solution was then transferred to a three-necked flask and 0.5g of hydroxylated boron nitride, 0.2g of dopamine hydrochloride and 0.12g of ammonium persulfate were added thereto in mass ratio. And (3) after the mixed solution is uniformly stirred by ultrasound, stirring and reacting for 10 hours under the condition of water bath heat preservation at the temperature of 60 ℃, filtering and washing by using deionized water, and drying for 10 hours at the temperature of 80 ℃ to obtain the dopamine modified boron nitride.
Step two: 1.08g of polyamic acid was added to a beaker containing 40.5ml of a 5mg/ml dopamine-modified boron nitride dispersion and 13.5ml of a 5mg/ml hydroxylated carbon nanotube dispersion, and 1.485ml of triethylamine was added thereto and stirred. Wherein the mass ratio of the polyamic acid to the dopamine modified boron nitride to the hydroxylated carbon nanotube is 80: 15: 5.
And after completely stirring and dissolving, pouring the solution into a mold, placing the mold in a four-directional freezing device for freezing for 30min for molding, then transferring the mold into a vacuum freeze dryer for processing for 72 hours, taking out a sample, placing the sample in a tubular furnace, and carrying out imidization under the protection of nitrogen. The imidization condition is that the sample is heated to 80 ℃, 150 ℃ and 250 ℃ in sections at the speed of 8 ℃/min from room temperature, and the temperature is continuously kept for 1 hour in each section, so as to obtain the polyimide/dopamine modified boron nitride/hydroxylated carbon nanotube composite aerogel.
The structure of the four-directional freezing device adopted in this embodiment is schematically shown in fig. 1, and a square-shaped freezing tank is adopted, and the freezing tank is of a hollow square-shaped structure and is opened at one corner position so as to facilitate the addition of liquid nitrogen. Wherein, the external dimension of the square-shaped freezing tank is 9.5cm multiplied by 3cm, the middle dimension is 3cm multiplied by 3cm, and the dimension of a liquid nitrogen charging opening is 1cm multiplied by 1 cm. In the freezing preparation process, the cold source is uniformly transmitted to the mould from positive and negative directions of an X, Y shaft through the zigzag freezing groove.
The polyimide/dopamine modified boron nitride/hydroxylated carbon nanotube composite aerogel prepared in the embodiment has a stress of 40kpa under 70% compressive strain and a thermal decomposition temperature of 475 ℃. Therefore, the polyimide/dopamine modified boron nitride/hydroxylated carbon nanotube composite aerogel has good mechanical properties and thermal stability.
Fig. 2 is a graph of water contact angle as a function of time for aerogels prepared in example 1, example 2, and example 4. It can be seen from the graph that the aerogel prepared in example 1 has a contact angle of 122.99 deg., and exhibits hydrophobicity with a contact angle of 2s unchanged. The contact angle of the composite aerogel prepared in the examples 2 and 4 is less than 90 degrees after 2s, and the composite aerogel shows better hydrophilicity
Fig. 3a and b are SEM photographs (both from the perspective of the plane of the Z-Y axis in fig. 1) of the aerogels prepared in example 3 and example 4, respectively. As can be seen from the figure, the aerogel prepared in example 4 has a low-curvature vertical tube hole structure (b) relative to the aerogel prepared in example 3.
FIG. 4 is at 2kW/m2The surface temperature of the aerogels prepared in examples 1, 2 and 4 under xenon light exposure is plotted against time. It can be seen from the figure that the surface equilibrium temperatures of the aerogels prepared in example 1, example 2 and example 4 are 55.5 ℃, 82 ℃ and 124.9 ℃, respectively, and thus it can be seen that the aerogel prepared in example 4 has higher thermal conversion capability.
FIG. 5 is a graph showing the comparison of ion concentrations before and after the purification of high-concentration metal ion wastewater by the aerogel prepared in example 4. As can be seen from the figure, the initial concentrations are all 106Mu g/L of Cu-containing2+、Cr3+、Mn2+、Ni+、Zn2+After the sewage is purified by the aerogel prepared in the embodiment 4, the ion concentration of the sewage is respectively reduced to 3.4, 0.5, 3.2, 5.9 and 2.1 mu g/L, and the sewage reaches the drinking water standard. Therefore, the aerogel has good purification capacity on sewage containing high-concentration metal ions.
Example 5
The method comprises the following steps: 0.12g of tris powder was dissolved in 100ml of deionized water and the solution pH was adjusted to 4.5 with dilute hydrochloric acid. The solution was then transferred to a three-necked flask and 0.5g of hydroxylated boron nitride, 0.2g of dopamine hydrochloride and 0.12g of ammonium persulfate were added thereto in mass ratio. And (3) after the mixed solution is uniformly stirred by ultrasound, stirring and reacting for 10 hours under the condition of water bath heat preservation at the temperature of 60 ℃, filtering and washing by using deionized water, and drying for 10 hours at the temperature of 80 ℃ to obtain the dopamine modified boron nitride.
Step two: 1.08g of polyamic acid was added to a beaker containing 45.9ml of a dopamine-modified boron nitride dispersion having a concentration of 5mg/ml and 8.1ml of a hydroxylated carbon nanotube dispersion having a concentration of 5mg/ml, and 1.485ml of triethylamine was added thereto and stirred. Wherein the mass ratio of the polyamic acid to the dopamine modified boron nitride to the hydroxylated carbon nanotube is 80: 17: 3.
And after completely stirring and dissolving, pouring the solution into a mold, placing the mold in a four-directional freezing device for freezing for 30min for molding, then transferring the mold into a vacuum freeze dryer for processing for 72 hours, taking out a sample, placing the sample in a tubular furnace, and carrying out imidization under the protection of nitrogen. The imidization condition is that the sample is heated to 80 ℃, 150 ℃ and 250 ℃ in sections at the speed of 8 ℃/min from room temperature, and the temperature is continuously kept for 1 hour in each section, so as to obtain the polyimide/dopamine modified boron nitride/hydroxylated carbon nanotube composite aerogel.
FIG. 6 is at 2kW/m2The water evaporation rates of the aerogels prepared in examples 1, 3, 4 and 5 under xenon light exposure are plotted versus time. As seen from the graph, the water evaporation rates of the aerogels prepared in example 1, example 3, example 4 and example 5 were 0.3, 1.7, 1.9 and 1.6L/(m)2H). Therefore, the aerogel prepared in example 4 has better water evaporation performance.
Example 6
The method comprises the following steps: 0.12g of tris powder was dissolved in 100ml of deionized water and the solution pH was adjusted to 4.5 with dilute hydrochloric acid. The solution was then transferred to a three-necked flask and 0.5g of hydroxylated boron nitride, 0.2g of dopamine hydrochloride and 0.12g of ammonium persulfate were added thereto in mass ratio. And (3) after the mixed solution is uniformly stirred by ultrasound, stirring and reacting for 10 hours under the condition of water bath heat preservation at the temperature of 60 ℃, filtering and washing by using deionized water, and drying for 10 hours at the temperature of 80 ℃ to obtain the dopamine modified boron nitride.
Step two: 1.08g of polyamic acid was added to a beaker containing 51.3ml of a 5mg/ml dopamine-modified boron nitride dispersion and 2.7ml of a 5mg/ml hydroxylated carbon nanotube dispersion, and 1.485ml of triethylamine was added thereto and stirred. Wherein the mass ratio of the polyamic acid to the dopamine modified boron nitride to the hydroxylated carbon nanotube is 80: 19: 1.
And after completely stirring and dissolving, pouring the solution into a mold, placing the mold in a four-directional freezing device for freezing for 30min for molding, then transferring the mold into a vacuum freeze dryer for processing for 72 hours, taking out a sample, placing the sample in a tubular furnace, and carrying out imidization under the protection of nitrogen. The imidization condition is that the sample is heated to 80 ℃, 150 ℃ and 250 ℃ in sections at the speed of 8 ℃/min from room temperature, and the temperature is continuously kept for 1 hour in each section, so as to obtain the polyimide/dopamine modified boron nitride/hydroxylated carbon nanotube composite aerogel.
The foregoing is merely exemplary and illustrative of the principles of the present invention and various modifications, additions and substitutions of the specific embodiments described herein may be made by those skilled in the art without departing from the principles of the present invention or exceeding the scope of the claims set forth herein.
Claims (9)
1. The polyimide composite aerogel is characterized by being formed by uniformly dispersing dopamine modified boron nitride and hydroxylated carbon nanotubes in a polyimide matrix and presenting a low-bending vertical pipe hole structure.
2. A method for preparing the polyimide composite aerogel according to claim 1, comprising the steps of:
the method comprises the following steps: preparation of dopamine modified boron nitride
Dissolving tris powder in deionized water, adjusting the pH value of the solution by using dilute hydrochloric acid, then adding a hydroxylated boron nitride nanosheet, dopamine hydrochloride and ammonium persulfate into the solution, stirring uniformly by using ultrasonic waves, continuing stirring and reacting under the condition of water bath heat preservation, and finally washing and drying to obtain dopamine modified boron nitride powder;
step two: preparation of polyimide/dopamine modified boron nitride/hydroxylated carbon nanotube composite aerogel
Respectively dispersing dopamine modified boron nitride powder and a hydroxylated carbon nanotube into deionized water, mixing and ultrasonically stirring uniformly, then adding polyamide acid into the mixed dispersion liquid, adding triethylamine, stirring and dissolving completely, adopting a four-directional preparation process, freezing and molding the mixed solution in a mold by using liquid nitrogen, and then sequentially carrying out vacuum freeze drying and imidization to obtain the polyimide/dopamine modified boron nitride/hydroxylated carbon nanotube composite aerogel.
3. The method of claim 2, wherein the concentration of the tris solution in the first step is 1-1.5 g/L, the mass ratio of the tris powder to the hydroxylated boron nitride nanosheets is 2-3: 10, and the pH value of the tris solution is adjusted to 4-5 by 1mol/L of dilute hydrochloric acid.
4. The method of claim 2, wherein the mass ratio of the hydroxylated boron nitride nanosheets, dopamine hydrochloride and ammonium persulfate in step one is 25: 10: 6.
5. The method of claim 2, wherein the ultrasonic stirring is performed uniformly in the step one, and then the stirring reaction is continued for 10-14 hours under the condition of water bath heat preservation at 55-65 ℃.
6. The method of claim 2, wherein the mass ratio of the polyamic acid to the triethylamine in the second step is 1: 1, the mass ratio of the polyamic acid to the dopamine modified boron nitride + hydroxylated carbon nanotube is 80: 20, and the mass ratio of the dopamine modified boron nitride to the hydroxylated carbon nanotube is 3-19: 1.
7. The method as claimed in claim 2, wherein in the second step, a four-directional preparation process is adopted, the mixed solution in the mold is frozen by liquid nitrogen for 15-60 min for molding, and then vacuum freeze drying is carried out for 48-96 h.
8. The method of claim 2, wherein the vacuum freeze-drying in step two is followed by imidization in a tube furnace under nitrogen protection under the following imidization conditions: heating the sample from room temperature to 80 ℃, 150 ℃ and 250 ℃ in sections at a heating rate of 8 ℃/min, and continuously preserving heat for 1h in each section to finally obtain the polyimide/dopamine modified boron nitride/hydroxylated carbon nanotube composite aerogel.
9. Use of the polyimide composite aerogel according to claim 1 as a solar evaporator.
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| CN114750491A (en) * | 2022-05-24 | 2022-07-15 | 陕西科技大学 | Polydopamine modified boron nitride nanosheet/polyimide heat-conducting and insulating composite film and preparation method and application thereof |
| CN114989608A (en) * | 2022-07-01 | 2022-09-02 | 宁夏清研高分子新材料有限公司 | Heat-conducting polysulfone composite material and preparation method thereof |
| CN115651265A (en) * | 2022-11-04 | 2023-01-31 | 西北工业大学 | Preparation method of polyimide fiber-based photo-thermal aerogel with asymmetric wettability |
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| CN115651265B (en) * | 2022-11-04 | 2024-01-30 | 西北工业大学 | Preparation method of asymmetric wettability polyimide fiber-based photo-thermal gel |
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